Diesel exhaust smell

[captaingary]

I have a strong odor of partially burned diesel coming from the exhaust on a Universal M35A motor. I ran a compression test and all cylinders are all equal but test 290psi. The manual calls for 448psi with a limit of 337psi. Any suggestions?

[Dale Thompson]

Gosh, I thought that was normal.  Especially motoring down wind.  Unless there is also a lot of black smoke, I don't believe there is a problem.  When I try to overpower by going over my hull speed, the black smoke starts to show.  It's been my experience that diesels smell and that's their nature.

If it is inside your after cabin, that's different..... and maybe potentially serious.

[john meyer]

Gary, I can't help you on the compression tests but it's a chance for me to put in my plug for Bio Diesel.  I've been burning this stuff for two years  with no issues.  The little fuel I burn negates the extra cost.   The claim is that my exhaust will smell like french fries (which would be OK with me) but in actuality my exhaust has little or no odor at all.

[Randy and Mary Davison]

After smelling strong diesel under the dodger while motoring, I tried putting our carbon monoxide detector at various spots under the dodger.  Sure enough, when conditions are right, the detector will see up to 50 units.  Can't remember what the scale is.  It's not enough to set off the alarm but may explain the headaches we both get sometimes when motoring.

Now we open the zippers in the front of the dodger to let fresh air flow through.  The detector goes to 0 and the headaches disappear.  I'm assuming this is the same thing that happens in a car or van when you leave the hatchback open.

I've never detected any CO in the cabin but we always have some air flowing through.

[Ray & Sandy Erps]

Gary,

Is this a new development?  Any problems starting the engine?  Has it overheated recently or been run low on oil?  How many hours are on the motor?  Any indications of excessive oil or coolant leaking from the head gasket area?  What color is the exhaust smoke?

My off the cuff guess would be that if the motor starts and runs fine, that your low compression readings aren't too much of a concern.  I would look over the transom while the engine is running and look for an oily sheen on the water to try and get an idea if unburnt diesel is making it through the combustion chamber.  Seems like the motor would be running bad if unburned diesel was in the exhaust.

Like the others have said, we get an exhaust backdraft into the cockpit when motoring with the dodger closed up.  We generally have to crack open the windscreen a little bit to let some air flow through as well or sit on the combing depending on the wind direction.

Ray

[APACHE]

Gary : I think that you need to pose that question to Westerbeake, a Universal dealer or your local Kubota tractor mechanic.  

[captaingary]

I tested the compression again today after squirting a little oil in each cylinder. The compression came up to 400 pounds each. What next?

[Ray & Sandy Erps]

Gary,

Can't offer much in the way of suggestions without a better idea of the symtoms.  Does the engine start okay?  Does it run okay?  Is there much smoke and what kind of smoke?  Is the odor raw fuel, or diesel exhaust?  Has the engine been overheated or run low on oil?

As many have already stated, a diesel exhaust odor isn't unusual, especially with a dodger that creates a back draft into the cockpit.  As to your first compression test, if the engine starts fine, I would be suspicious of the results of the first test.  A diesel engine needs a fair amount of compression to develope enough heat to start and continue to run in the first place.  White smoke is an indication of unburnt fuel in the exhaust, not to be confused with some white steam.

[Ken Juul]

The piston rings need a bit of oil on the cylinder walls to help with the seal.  I would assume on your first test it was a cold engine that was sitting for a while.  Before testing compression in any engine, running it for a couple minutes or cranking with no ignition (Pull coil wire or compression release) should get the cylinders lubricated.  Your squirting the oil did the same thing.  I think it is fine.  

I can't ever remember smelling exhaust in the cockpit.  Wish I knew what I was doing differently so I could pass it on.  We have the standard Dodger/bimini set up, about 800 hrs on our Mk25x.

[Randy and Mary Davison]

Ken,

We don't have a bimini on Gorbash (no sun to hide from in the NW).  Maybe that changes the airflow somehow although I would have guessed a bimini would make it worse by creating more of a tunnel.